In a hard disk drive (HDD) having a magnetic disk, a magnetic head records on and reproduces the magnetic disk keeping a space from the magnetic disk, in other words, flying over the magnetic disk. However, due to temperature, humidity, or altitude of the environment in which the HDD is used or a partial protrusion and the like on the magnetic disk, flying height control may not be carried out properly resulting in a touchdown where the head comes in contact with the magnetic disk.
When such a touchdown occurs, a recording error or a reproduction error may occur caused by high flying of the head, deterioration of head positioning accuracy, high-temperature demagnetization due to heat generated by the contact, or other phenomena associated with the touchdown. Therefore, the flying height of the head with respect to the magnetic disk requires a highly precise designing in the manufacturing process of the HDD so that the touchdown is prevented from occurring under the environment of the HDD usage of the user.
Meanwhile, in recent years, the capacity of magnetic disks has been becoming larger due to high density recording. To realize the recording in high density on the magnetic disk, it is necessary to reduce the flying height of the head from the magnetic disk to the minimum level. Accordingly, with a larger capacity of the magnetic disk, the possibility of an unintended touchdown occurring due to changes in external environment and the like is increasing.
When a touchdown occurs under the environment of the HOD usage of the user, a special process of recording or reproduction needs to be performed again (retry process). In conventional art, however, it is difficult to detect a touchdown and to perform the retry process of recording or reproduction when the touchdown occurs under the environment of the HDD usage of the user.